Shiga Toxins Stimulate Secretion of Interleukin-8 from Intestinal Epithelial Cells

Abstract

In the 1980s, Shiga toxin (Stx)-producing Escherichia coli O157:H7 (STEC) was identified as a cause of hemorrhagic colitis in the United States and was found to be associated with hemolytic uremic syndrome (HUS), a microangiopathic hemolytic anemia characterized by thrombocytopenia and renal failure. The precise way that Stxs cause hemorrhagic colitis and HUS is unclear. Stxs have been thought to cause disease by killing or irreversibly harming sensitive cells through a nonspecific blockade of mRNA translation, eventually resulting in cytotoxicity by preventing synthesis of critical molecules needed to maintain cell integrity. Because STEC is noninvasive, we have been exploring the host-toxin response at the level of the gastrointestinal mucosa, where STEC infection begins. We have found that Stx is capable of interleukin-8 (IL-8) superinduction in a human colonic epithelial cell line. Despite a general blockade of mRNA translation, Stx treatment results in increased IL-8 mRNA as well as increased synthesis and secretion of IL-8 protein. Our data suggest that an active Stx A subunit is required for this activity. Ricin, which has the same enzymatic activity and trafficking pathway as Stx, has similar effects. Exploration of the effects of other protein synthesis inhibitors (cycloheximide, anisomycin) suggests a mechanism of gene regulation that is distinct from a general translational blockade. Use of the specific p38/RK inhibitor SB202190 showed that blocking of this pathway results in decreased Stx-mediated IL-8 secretion. Furthermore, Stxs induced mRNA of the primary response gene c-jun, which was subsequently partially blocked by SB202190. These data suggest a novel model of how Stxs contribute to disease, namely that Stxs may alter regulation of host cell processes in sensitive cells via activation of at least one member of the mitogen-activated protein kinase family in the p38/RK cascade and induction of c-jun mRNA. Stx-induced increases in chemokine synthesis from intestinal epithelial cells could be important in augmenting the host mucosal inflammatory response to STEC infection.

Real-time 2-5A kinetics suggest that interferons β and λ evade global arrest of translation by RNase L

“…Of note, anisomycin had a mild stimulatory effect on ISG mRNAs due to an unknown mechanism; this effect acted in the opposite direction of blocking IFNs and thus did not affect the suitability of anisomycin as a control in our tests. The observation that translation inhibitors, such as anisomycin or cycloheximide, can induce cytokines has been reported previously (40,41). Taken together, our experiments indicate that IFNs are indeed translated when the bulk of protein synthesis remains silenced by 2-5A.…”

Role of EHEC O157:H7 virulence factors in the activation of intestinal epithelial cell NF-κB and MAP kinase pathways and the upregulated expression of interleukin 8

“…3, increased phosphorylation of p38 MAP kinase occurred within 1-2 h of infection with wild-type EHEC. As Stx-2 had been reported to activate p38 (Thorpe et al, 1999), we asked whether p38 phosphorylation required Stx-2. As shown in Fig.…”

Shiga toxin 1-induced cytokine production is mediated by MAP kinase pathways and translation initiation factor eIF4E in the macrophage-like THP-1 cell line

“…The localized production of TNF-␣ and IL-1␤ may contribute to pathogenesis by upregulating the expression of Gb3 on target endothelial cells, thereby sensitizing the cells to the action of Stxs [16 -18]. Chemokines may be essential for the infiltration of monocytes and neutrophils into sites of vascular damage [15,19].…”